Gasoline composition



United States Patent 3,098,688 GASGHNE CUMPOSITIGN Reid E. Sutton andJohn L. Esme, East Alton, BL, as-

signors to Shell Oil Company, New York, Nfifl, a corporation of DelawareNo Drawing. Filed Mar. 29, 1969, Ser. No. 13,257

6 Claims. (til. 4469) This invention relates to improved hydrocarbonfuel compositions and particularly to improved motor gasoline fuelcompositions having high octane numbers.

Recent automotive design trends have been toward engines having greaterpower for the same size engine and more elhcient utilization of thegasoline fuel. Engine designers have accomplished this largely bysteadily raising the compression ratios of automotive engines, which hasnecessitated the use of fuels having increased resistance to detonationor spark knock. There is also an increased demand for aviation fuelshaving greater antiknock properties. It has heretofore been possible tomanufacture such fuels from crude petroleum by the development andutilization of new hydrocarbon conversion and synthesis processes suchas cracking, reforming, polymerization, and alkylation. The resistanceto knock of the fuels from these processes is even further aug mented bythe addition of antiknock agents such as tetraethyllead (TEL), and,recently, metbylcyclopentadienyl manganese tricarbonyl. Resistance tospark knock is, of course, evaluated as octane number. Therefore, thedemand for fuels having greater resistance to spark knock is manifestedin the constantly increasing octane number of premium fuels. However, asthe octane number of modern gasoline fuels has been raised, there hasbeen a concomitant decrease in the susceptibility of such fuels tooctane number improvement by addition of organometallic antiknockagents. It becomes less economical, therefore, to obtain greaterresistance to spark knock by this means with higher octane number fuels.In addition, the amount of organo-metallic additive which is added tomotor fuels may also be limited by consideration of the degree oftoxicity imparted to the fuel containing such materials. For thisreason, the maximum amount of tetraethyllead which may be added tocommercial gasoline motor fuels is 3 or 4 cc./ gal. (U.S.) and 6 cc./gal. (U.S.) for automotive and aviation fuels, respectively.Consequently, the degree of octane number improvement which can beobtained in this manner is limited. Organo-metallic antiknock additivesare difficult to synthesize and are expensive. Their addition to fuelsis thus limited to small concentrations by considerations of ecomonicsas well. Yet another limitation on the use of such antiknockadditive-containing fuels is the tendency of the antiknock additivestherein to lay down large quantities of deposits in the combustionchamber of the engine, which may contribute to an increase in the octanenumber of requirement of the engine. Because of these limiting factorson the use of conventional organo-metallic antiknock additives, theoctane number obtainable from gasoline fuels made by conventionalrefining processes has also been limited.

There have been many attempts to solve this problem by the use of two ormore antiknock agents. However, in most of these situations, theincremental increase in octane number obtained by adding the secondantiknock agent has been considerably :less than the octane numberincrease obtainable when the supplemental antiknock agent is added tothe gasoline by itself. That is, the antiknock activity of thesupplemental antiknock agent or of both antiknock agents is less, on thebasis of the volume added, than either by itself. Consequently, eventhough significant increases in octane number are obtainable, it hasheretofore been uneconomical to obtain higher octane number motorgasoline in this manner.

It is therefore an object of this invention to provide improved gasolinefuel compositions. It is also an obect of the invention to augment theefficacy of tetraethyllead as an antiknock additive in gasoline. It is afurther object of the invention to provide higher antiknock qualityingasoline in an economical manner. It is still another object to providehydrocarbon compositions which enhance the efiiciency of antiknockadditives added thereto. Another object is to attain the foregoingobjects without detrimental side eifects in the use of the fuel ingasoline engines. A still further object of the invention is to providean improved antiknock additive concentrate composition.

The attainment of these and other objects will be apparent from thedetailed description of the invention which is a gasoline motor fuelcomposition containing a tetraalkyllead compound as a primary antiknockagent and small but critical amounts of certain aromaticchrotricarbonyls which by themselves exhibit no primary antiknockactivity.

The use of organo-metallic compounds as primary antiknock agents haslong been known, and countless numbers of these materials have beensuggested, tried, and used with various degrees of success. The mostwidely used for many reasons, including availability, economy, andantiknock activity, are the tetraalkylleads, particularly tetraethylleadand tetramethyllead. However, it has now been found that certainaromatic chromimn tricarbonyls, which possess essentially no primaryantiknock activity when they are added to gasoline containing no otherantiknock agent, nevertheless when added to leaded gasoline-s ofselected composition as to hydrocarbon type and boiling range possess anextraordinary and unexpected co-antiknock activity. By co-antiknockactivity, it is here meant that the secondary or co-antiknock agentcauses the octane number of the gasoline containing both primary andsecondary antiknock additives to be raised significantly above the levelwhich is obtained by the primary antiknock agent alone, the co-antiknockeffect being the result of co-action of the secondary with the primaryadditive rather than any primary antiknock properties of the secondaryadditive alone.

The addition of very small amounts of aromatic chromium tricarbonyls tofuels containing tetraalkyllead primary antiknock agents has been foundto raise the octane number of the total mixture by as much as 5.0 octanenumbers.

The aromatic chromium tricarbonyl s which have been found to beeffective co-antiknock agents with tetraalkyllead are represented by theempirical formula ACr(CO) wherein A is a monoaromatic compoundcorresponding to the following formula:

Within the context of the above formula, three of the Rs are monovalentradicals selected from H and CH while one of them is a monovalentradical selected from 'H: n 2n+h OR:

n 1| M ii -ooR, OGOR, -ooR, -CR

wherein n is a whole number from 1 to 4- inclusively, and

3 the Rs'are H, CH or together are tetramethylene (CH CH CH CH Theforegoing class of aromatic chromium tricarbonyls, which are believed tobe complexes, may be prepared by displacement of CO from Cr(CO) by thearomatic. Examples of such aromatic chromium tricarbonyls which havebeen prepared and which may be used according to the invention are thoseaccording to the formula ACr(CO) in which A is benzene, toluene,o-xylene, m-xylene, p-xylene, mesitylene, hexamethylbenzene,tetrahydronaphthalene (tetralin), methoxy-benzene (anisole), methylo-tolyl ether, methyl p-tolyl ether, aminobenzene (aniline),o-toluidine, m-toluidine, p-toluidine, N-methylaniline,NNdimethylaniline, NNdimethylotoluidine, methyl benzoate, benzylalcohol, acetophenone, tert.-butylbenzene, phenyl acetate.

The extraordinary co-antiknock action of this unique class of complexesmay best be seen by reference to the following example:

EXAMPLE I A number of aromatic chromium tricarbonyls, each within theforegoing described class, were added to separate samples of acommercial gasoline blending component having a boiling range belowabout 400 F. and which had previously been leaded to a level of 3 cc.tetraethyllead (TEL) per US. gallon. The octane number of all thesamples containing the co-antiknock or secondary additive and also aseparate sample of each of the same gasoline blending componentscontaining only 3 cc. TEL/ gal. (U.S.) were determined by the ResearchMethod (ASTM test designation D-357-53). To determine the increase inoctane number obtained by adding small amounts of co-antiknock agent,the difierence in the octane numbers of the samples with and withoutcoantiknock agent (AO.N.) were calculated. The results ore tabulated inthe following Table I.

Table l Coneen- Metal Octane tration ratio number Secondary antiknockagent (milli- (gins. Or/ enhancemoles/ gm. Pb) merit gal.) (A O.N.)

Mesitylene chromium tricarbonyl l 016 2. 4 2 .033 3. 4 065 1. 7 8 131 0.7 Mesitylene chromium tricarbonyl 1 016 5. 0 2 033 3. 7 Toluene chromiumtricarbonyl 1 016 0.2 2 033 1. 2 4 .065 2.9 8 131 3 6 Ortho xylenechromium triearbonyl 1 016 2.0 2 033 2. 6 8 .131 0.0

1 In olefin-isobutano alkylate. 2 In blend of naphthenes: equal volumesof cyclohexane, cyelopentane,

and methyl cyclopentane.

EXAMPLE II Mesitylene chromium tricarbonyl was added in variousconcentrations to separate samples of the same olefinisobutane alkylatewhich had been employed in the previous example, but which contained noprimary antiknock agent. a The Research octane numbers of these samplesbe operable.

were then compared with the previously determined octane numbers of thealkylate which contained no additives of any kind. The results were asfollows:

Table II ANTIKNOCK ACTION OF AROMATIC CHROMIUM TRIC'ARBONYL WITHOUTTETRAALKYLLEAD Octane Number Concentration (millimoles/gal): enhancement(AO.N.) 5 -0.3 10 -0.4

Thus, it may be seen that the aromatic chromium tricarbonyls are in factpro-knock agents in the absence of tetraalkyllead primary antiknockagents, which indicates clearly that their eflicacy as antiknock agentsarises from their cooperative action or co-action with the lead primaryanti'knock agents. Though analogous aromatic metal tricarbonyls can alsobe prepared from molybdenum and tungsten, these materials have beenfound to possess no antiknock activity either primary or secondary.

Referring once again to Table I, it will be observed that theeffectiveness of the aromatic chromium tricarbonyls varies considerablywith their concentration in the blend, and, concomitantly with the ratioof co-antiknock agent to tetraethyllead. These data indicate that thesecondary antiknock agents are effective in concentrations as small as0.5 millimole per gallon. The upper limit at which antiknock efiects areobtained, however, varies considerably with the particular co-antiknockagent which is used. For example, while rnesitylene and ortho xylenechromium tricarbonyls appear to be ineifective above about 6 or 7millimoles per gallon (U.S.), toluene chrominrn tricarbonyl is effectiveat much higher concentrations, for example, up to about 15 millimolesper gallon. Even so, the maximum benefit obtainable in gasolinecontaining 3 cc. TEL per gallon will be obtained at co-antiknockconcentrations of less than about 15 millimoles per gallon.

The concentration of the co-antiknock agent is more meaningful, however,when it is expressed in relation to the amount of primary antiknockagent which is used therewith. It has been found that the optimumconcentration of the co-antiknock agents is the gasoline compositions ofthe invention is approximately proportional to the amount of primaryantiknock agent also used in the gasoline. This phenomenon, of course,still further indicates the cooperative action of the co-antiknockagents with tetraalkyllead. The amount of co-antiknock agent relative tothe primary antiknock agent is most conveniently expressed in terms ofthe metal ratio which is defined and used hereinafter to mean the weightratio of metal (chromium) contained in the co-antiknock agent to metal(lead) contained in the tetraalkyllead primary antiknock agent. Thus,the aromatic chromium tricarbonyls are effective to raise the octanenumber of leaded gasoline when the metal ratio of the two antiknockadditives is at least 0.01 gram of chromium contained in theco-antiknock agent present per gram of lead contained in the primaryantiknock agent present. A minimum metal ratio of 0.015 is preferred.

The maximum metal ratio at which the co-antiknock additives may beemployed to obtain significant co-antiknock benefits varies considerablyamong the various aromatic chromium tricarbonyls which have been foundto, However, in each case this maximum ratio.

1 will not exceed about 0.25 gm. Cr/gm. Pb. Moreover,

it is preferred to that the metal ratio not exceed about 0.15. Thus thefuel compositions of the invention contain an octane number-improvingamount of co-antiknock agent which corresponds to a metal ratio of atleast 0.015 but not more than about 0.15 gram of chromium per gram oflead.

Though in the foregoing examples tetraethyllead was employed inconcentrations of 3 cc./ gal. (U.S.), it will be recognized that thefuel compositions in accordance with the invention may contain anyoctane number-improving amount of tetraethyllead, e.g. as low as 0.5 cc.TEL/ gal. to as high as 12 cc. TEL/gaL, so long as the metal ratio iskept within the foregoing discussed limits.

From the preceding discussion and data, it is apparent that the aromaticchromium tricarbonyls are highly effective as co-antiknock agents inisoparafiinic and naphthenic hydrocarbons. However, their use asco-antiknock agents is not limited thereto. The composition of the basefuel to which they are added does, however, exert a profound eifect ontheir activity as co-antiknock agent with tetraalkyllead compounds.

Efiec! iso and normal parafiins 0n co-antiknock activity-The addition oflight isoparafiins, i.e., those having less than 8 carbon atoms permolecule, is beneficial to the action of the co-antiknock agent.However, the addition of heavier isoparaffins reduces the co-antikuockeffect considerably. It is therefore preferred that the gasolinecompositions in accordance with the invention not contain greater thanabout 20% by volume of isoparafiins boiling over about 300 F. It is evenfurther preferred that the gasoline composition contain no more thanabout 10% by volume of isoparafiins boiling above about 300 F.

Because of the detrimental effect of normal parafiins in reducing theoctane number, the gasoline compositions in accordance with theinvention preferably contain essentially no normal paratfins having 7 ormore atoms per molecule and only small amounts, preferably not over 10%,of normal paraffins having or 6 carbon atoms per molecule. Fuelcompositions containing essentially no normal parafiins having 5 or morecarbon atoms per molecule are particularly preferred. Normal paraffinshaving less than 5 carbon atoms per molecule, for example, normalbutane, having high octane numbers, are useful to provide the gasolinewith proper vapor pressure and are not deleterious to the action of theco-antiknock agents.

Efiecr of cyclopamfl'ins (naphthenes).'1he gasoline compositions of theinvention should contain no more than by volume naphthenes boiling aboveabout 300 F., and preferably substantially none, because they aredeleterious both with regard to blending octane number and their effecton the response of the co-antiknock agent. There is no limit, however,in the broad aspects of the invention, to the maximum concentration ofnaphthenes boiling below about 300 F.

Efiect of olefins on co-antiknock activizy.'Ihe incorportion of up toabout 10% of lighter olefins, especially those which are branched, isactually beneficial to the co-action of the co-antiknock agents withtetraethyllead. Moreover, the gasoline compositions of the invention canadvantageously contain up to 30% by volume olefins, but largerquantities are deleterious and should be avoided.

Efiect of aromatics-Aromatics boiling below about 300 F., i.e., Caromatic hydrocarbons and lighter, have been found to be not greatlydeleterious in minor concentrations, e.g., below about 50% by volume.Heavier aromatics, however, which boil above about 300 F. aredeleterious and should not exceed about 20% by volume of the totalgasoline blend. In fact, in order to obtain more practical benefits fromthe co-antiknock agent, it is preferred that the gasoline of theinvention contain no more than about 10% by volume of aromatics boilingabove 300 F., and no more than 30% by volume of total aromatics.

Though the deleterious effect of high boiling aromatics on theeffectiveness of the co-antiknock additives is quite unfortunate, it hasbeen found that a very surprising relationship exists between the effectof heavy aromatics and the presence of light naphthenes. That is, lightnaphthenes suppress the deleterious effects of heavy aromatics. Inaccordance with applicants copending patent application Serial No.18,255, it is possible to have substantial amounts of aromatics boilingabove 300 in a base gasoline and still obtain large benefits fromco-antiknock additives, as long as light naphthenes, i.e., naphthenesboiling below about 300 F., are also incorporated in the base gasoline.

Relatively high response is obtained in light naphthenes even in thepresence of heavy aromatics. In general it appears that one volumepercent of light naphthenes can overcome completely the deleteriouseffect of one volume percent of heavy aromatics. However, sincepractical benefits are obtained up to 10% and 20% by volume heavyaromatics even in the absence of naphthenes, it is not necessary alwaysto have present as much light naphthenes as would be needed tocompletely cancel the eflfect of the heavy aromatics. The lightnaphthenes can be used to obtain even greater benefits from theco-antiknock additives in gasoline which must contain aromatics boilingabove 300 F., to have proper volatility distribution of high octanenumber components. To take advantage of light naphthenes in accordancewith this preferred aspect of the invention, it is desirable that thebase gasoline contain at least by volume, or preferably at least /2% byvolume, of naphthenes boiling below 300 F. for each 1% by volume ofaromatics boiling above 300 F. in excess of 10% by volume of sucharomatics, and preferably such amounts of light naphthenes for each 1%by volume of all of such aromatics.

The adverse effect of each of the deleterious or antagonisticcomponents, that is, aromatics, olefins, C plus normal parafiins andheavy naphthenes, is not, however, independent. Even with the use ofnaphthenes in accordance with above, the presence of two or more of suchantagonists in maximum concentrations can result in a fuel having littleor no response to the action of the co-antiknock agents. Suchnon-responsive hydrocarbon compositions may be avoided, however, if thecompositions meet the following empirical correlation which constitutesa limitation on the total equivalent amount of co-antiknock antagonists(A which may be present in the hydrocarbon blend:

A zpercent by volume of aromatics boiling below 300 F.

A =percent by volume of aromatics boiling above 300 F.

A =percent by volume of olefins A =percent by volume of C plus normalparaflins and naphthenes boiling above 300 F.

N =percent by volume of naphthenes boiling below Summing up its broadaspects, the invention therefore resides in the discovery that aromaticchromium tricarbonyls, as defined hereinbefore, are effective asco-antiknock agents with tetraethyllead when both are added to gasolineblends containing essentially no normal parafiins containing 7 or morecarbon atoms, no more than 10% by volume of C to C normal paraffins, nomore than 20% by volume of isoparafiins boiling above 300 F., no morethan 10% by volume of naphthenes boiling above 300 F., no more than 30%by volume olefins, no more than 50% by volume of total aromatics and nomore than 20% by volume of aromatics boiling above 300" F., thecomposition of the gasoline blend also being within the limits definedby the empirical relationship In the foregoing examples in which TEL wasused as primary anti-detonant, the TEL was added in the form of thecommercial motor mix which has the following composition.

7 The co-antiknock materials of the invention are, however, equallyefiective in leaded gasoline in which pure TEL, and no halohydrocarbonscavenger, is used, or in which the commercial aviation mix containingone theory of ethylene dibromide, and no ethylene chloride, is used.

Besides the aforementioned halgen-containing lead scavengers, the fuelcompositions of the invention can, and ordinarily will, contain otheradditives, for example, dyes, spark plug anti-foulants such astricresylphosphate, dimethyl xylyl phosphate, and diphenyl cresyl phosphate,combustion modifiers such as alkyl boronic acids and lower alkylphosphates and phosphites, oxidation inhibitors such asN,N'-disalicylal-1,2-propanediamine, and rust in hibitors such aspolymerized linoleic acids and N,Cdisubstituted imidazolines, and thelike.

It is to be understood that the order of mixing the various constituentsof the compositions of the invention is immaterial. For example, theco-antiknock compound may be added to a gasoline which already containsthe tetraalkyllead primary antiknock material. Likewise, theco-antiknock and primary antiknock compounds may be first mixed, stored,and handled as a concentrate, and added to the gasoline at a later time.A gasoline additive conwntrate of this latter type may also contain halogen scavenger and spark plug antifouling compound. Under othercircumstances, it may be desirable to mix the halogen scavenger and theprimary antiknock compound, or the primary antiknock and co-antiknocxcompounds, in the desired relative proportions and handle or store thismixture, with or without stabilizers, antifouling compounds, inhibitors,etc., as a concentrate for incorporation with the other components ofthe ultimate fuel composition.

An additive concentrate of this latter type will therefore contain from0.01 to 0.25 gram of metal in the co-antiknock agent per gram of lead inthe tetraalkyllead. Pref erably, such a concentrate contains from about0.015 to about 0.15 gram of metal per gram of lead. A typical ad ditiveconcentrate in accordance with the invention and containing both TELmotor mix and phosphorus compound for ignition control as well asco-antiknock agent has the following composition.

We claim as our invention: 1. A gasoline composition consistingessentially of a 0 mixture of hydrocarbons having an ASTM boiling rangebelow about 400 R, an octane number-improving amount of tetraalkylleadand an octane number-improving amount of an aromatic chromiumtricarbonyl co-antiknock agent corresponding to the formula ACr(CO)wherein A is a monoaromatic compound corresponding to the formulawherein the R groups are monovalent radicals, three of which areselected from the group consisting of H and CH and one of which isselected from the group consisting of -H and C H wherein n is a wholenumber of from 1 to 4 inclusive, and the R groups are selected from thegroup consisting of --H and -CH when separate and (CH when takentogether, the amount of said co-antiknock agent corresponding to fromabout 0.01 to about 0.25 gram of chromium contained in the .co-antiknockagent per gram of lead contained in the tetraalkyllead, said mixture ofhydrocarbons containing (1) no more than 50% by volume of aromatics, (2)no more than about 30% by Volume olefins, (3) no more than about 20% byvolume each of isoparafiins and aromatics boiling above about 300 F.,(4) no more than about 10% by volume each of normal parafiins having 5to 6 carbon atoms per molecule and naphthenes boiling above about 300F., and (5) essentially no normal paraffins having greater than 6 carbonatoms per molecule, and further characterized as having an equivalentamount of co-antiknock antagonists (A not exceeding 50+0.75N wherein Aand N are defined as hereinbefore in the specification.

2. The fuel composition of claim 1 containing (1) no more than 50% byvolume of aromatics, (2) no more than about 20% by volume each ofolefins and aromatics boiling above about 300 F., (3) no more than about10% by volume each of isoparaflins boiling above about 300 F. andnaphthenes boiling above about 300 F., and (4) essentially no normalparafiins having greater than 4 carbon atoms per molecule, and furthercharacterized as having an equivalent amount of co-antiknock antagonists(A not exceeding 50+'0.75N wherein A and N are defined as hereinbeforein the specification.

3. A gasoline composition consisting essentially of a mixture ofhydrocarbons having an AST M boiling range below about 400 E, an octanenumber-improving amount of tetraalkyllead and an octane number-improvingamount of mesitylene chromium tricarbonyl co-antiknock agent 7corresponding to from about 0.01 to about 0.25 gram of chromiumcontained in the co-antiknock agent per gram of lead contained in thetetraalkyllead, said mixture of hydrocarbons containing (1) no more than50% by volume of aromatics, (2) no more than about 30% by volumeolefins, (3) no more than about 20% by volume each of isoparafiins andaromatics boiling above about 300 F., (4) no more than about 10% byvolume each of normal paralfins having 5 to 6 carbon atoms per moleculeand naphthenes boiling above about 300 F., and

(5) essentially no normal par-afiins having greater than 6 carbon atomsper molecule, and further characterized as having an equivalent amountof co-antiknock antagonists (A not exceeding 50+0.75N wherein A and Nare defined as hereinbefore in the specification.

4. A gasoline composition consisting essentially of a mixture ofhydrocarbons having an ASTM boiling range below about 400 R, an octanenumber-improving amount of tetraalkyllead and an octane number-improvingamount of toluene chromium tricarbonyl co-antiknock agent correspondingto from about 0.01 to about 0.25 gram of chromium contained in theco-antiknock agent per gram of lead contained in the tetraalkyllead,said mixture of hydrocarbons containing (1) no more than 50% by volumeof aromatics, (2) no more than about 30% by volume olefins, (3) no morethan about 20% by volume each of isoparafiins and aromatics boilingabove about 300 F., (4) no more than about 10% by volume each of normalparafiins having 5 to 6 carbon atoms per molecule and naphthenes boilingabove about 300 F., and (5) essentially no normal parafiins havinggreater than 6 carbon atoms per molecule, and further characterized ashaving an equivalent amount of co-antiknock antagonists (A not exceeding50+0.75N wherein A and N are defined as hereinbefore in thespecification.

5. A gasoline composition consisting essentially of a mixture ofhydrocarbons having an ASTM boiling range below about 400 F., an octanenumber-improving amount of tetraalkyllead and an octane number-improvingamount of ortho Xylene chromium tricarbonyl co-antiknock agentcorresponding to from about 0. 01 to about 0.25 gram of chromiumcontained in the co-antiknock agent per gram of lead contained in'thetetraalkyllead, said mixture of hydrocarbons containing 1) no more than50% by volume of aroma-tics, (2) no more than about 30% by volumeolefins, 3) no more than about 20% by volume each of isoparafiins andaromatics boiling above about 300 F., (4) no more than about 10% byvolume each of normal paraftins having to 6 carbon atoms per moleculeand naphthenes boiling above about 300 F., and (5) essentially no normalparafiins having greater than 6 carbon atoms per molecule, and furthercharacterized as having an equivalent amount of co-antiknock antagonists(A not exceeding 50+0.75N wherein A and N are defined as hereinbefore inthe specification.

6. A gasoline additive concentrate composition consistiug essentially ofa mixture of tetraalkyllead and an aromatic chromium tricarbonylco-antiknock agent, the amount of co-antiknock agent corresponding tothe formula ACr(CO') wherein A is a mo-noaromat'ic compoundcorresponding to the formula wherein the R groups are monovalentradicals, three of which are selected from the group consisting of --Hand --CH and one of which is selected from the group consisting of -Hand -CnH wherein n is a whole number of from 1 to 4 inclusive, and the Rgroups are selected from the group consisting of H and CH when separateand (-CH when taken together, correspending to from about 0.01 to about0.25 gram of chrom ium contained in the co-antiknock agent per gram oflead contained in the tetraalkyllead.

References Cited in the file of this patent UNITED STATES PATENTS2,086,775 Lyons et al July 13, 1937 2,197,498 Guthmann Apr. 16, 19402,460,700 Lyons Feb. 1, 1949 2,818,416 Brown et al Dec. 31, 19572,875,223 Pedersen et al Feb. 24, 1958 2,913,413 Brown Nov. 17, 19593,001,858 Antonsen Sept. 26, 1961 OTHER REFERENCES A General Method ofPreparing Tricarbonylchrornium Derivatives of Aromatic Compounds, byNicholls et 211., Proceedings of the Chemical Society, London, May 1958,pp. 152 and 153.

Improved Motor Fuels Through Selective Blending, by Wagner et 211.,Paper presented before 22nd Annual Meeting of the American Petroleuminstitute, November 7, 1941, pp. -89.

Aviation Gasoline Manufacture, by Van Winkle, First Ed., 1944,McGraw-Hill Book Co., pp. 4363 and 197- 211.

1. A GASOLINE COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OFHYDROCARBONS HAVING AN ASTM BOILING RANGE BELOW ABOUT 400*F., AN OCTANENUMBER-IMPROVING AMOUNT OF TETRAALKYLLEAD AND AN OCTANE NUMBER-IMPROVINGAMOUNT OF AN AROMATIC CHROMIUM TRICARBONYL CO-ANTIKNOCK AGENTCORRESPONDING TO THE FORMULA ACR(CO)3, WHEREIN A IS A MONOAROMATICCOMPOUND CORRESPONDING TO THE FORMULA